well, presumably, when you "found the person you wanted to hire" initially, you went through the the interview process and interviewed plenty of candidates. (In Google's case, probably both foreign and domestic).

This second check is more of a "okay, so let's double-check". And yes, of course the advertisement is overly specific- haven't you seen job ads recently? When ads usually have that long list of requirements, they are usually advertising for a green card. Someone who occasionally interacts with mySQL suddenly is a mySQL master and so forth.